The present invention relates to a phosphorescent ink marking device, and particularly to an improved marking pen that utilizes a combination of a low viscosity ink, large phosphor particles having a short half-life of phosphorescence (afterglow), and certain capillary fiber writing nibs that allow flow of this low viscosity phosphor suspension during the process of writing on a substrate surface. The invention also relates to a method of using this marking pen and ink suspension to make notations which, after photo-excitation, can be used to expose photographic film (or other photosensitive surface) employed in laboratory autography procedures such as chemiluminescence autography and autoradiography.
Phosphorescent particle-dispensing pens and crayons, as well as phosphor-containing tape for laboratory use have been described in the prior art. These so-called “glow-in-the dark” marking devices have been used for producing written notations and/or alignment markings on laboratory autograms. Such autograms are typically produced using a sheet of X-ray film or any other radiation-sensitive or photo-sensitive surface (including a two dimensional electronic matrix reporting surface) that has been placed into contact with a laboratory material (experimental substrate) containing either radioactive isotope “tracer” materials or alternatively, light-emitting chemicals, i.e., chemiluminescent agents. For example, flat experimental substrates such as dried electrophoretic gels and molecular transfer blots are commonly exposed to X-ray films to generate autoradiograms. Phosphorescent marking devices have been used previously for marking such experimental substrate surfaces so that the resulting autoradiographic or chemiluminescent film exposure (autogram) can be oriented and matched with the original experimental substrate. Furthermore, phosphorescent notations may provide certain useful information about the experiment and materials therein, e.g., the date of the experiment, certain notebook references, etc.
Litt et al. in U.S. Pat. No. 4,510,392 describe a process of forming phosphor markings of trace metal-doped zinc sulfide on a substrate carrying radioactive isotope-tagged material, charging the phosphor with light, exposing these markings and radioactive material on the substrate to X-ray film, and finally developing the film to show the markings on the substrate. Generally, the phosphor has a particle size distribution peak of between 10 and 15 microns. While the inventors state that the ink formulation is not particularly critical, the ink is described as containing from 5-20% by weight of the phosphor, and the exemplary inks are formulated to be sufficiently viscous and dense to keep the phosphor particles suspended in the ink. The dispensing devices preferred for applying this ink include a capillary metal or plastic tube and ball-point pens (such as those formerly sold by E. I. Du Pont de Nemours and Company, Wilmington, Del., the assignee of U.S. Pat. No. 4,510,392). Problems associated with viscous phosphor-containing inks are discussed below. Typewriter ribbons and hard graphite compositions have also been mentioned as means for applying phosphor particles to experimental substrates.
A crayon-like phosphorescent autographic marking device carrying the same or similar phosphor particles suspended in a wax-like matrix material is commercially available from Bel-Art Products, Inc. (Pequannock, N.J.), and is used in the laboratory for similar purposes.
Perlman in U.S. Pat. No. 5,051,596 describes a phosphorescent marking tape adapted for use in laboratory autography. The tape includes a coating containing phosphor grains similar to those found in the ink of Litt et al. Black ink writing or other conventional opaque markings applied to the upper surface of the phosphorescent tape prevents phosphorescence from being emitted from the phosphor grains located beneath the markings. Accordingly, when the marked photon-emitting phosphorescent surface is placed against an X-ray film, the tape will expose an image of itself on the film except at the location of the markings (film development thus reveals clear markings against a dark image of the tape).
In developing the use of the phosphorescent marking tape, Perlman in U.S. Pat. No. 5,051,596 describes limitations in the use of prior art phosphorescent ink markers. For example, phosphorescent ink markers such as those described by Litt et al. in U.S. Pat. No. 4,510,392 tend to produce phosphor-containing written notations of non-uniform thickness. As a result, the autographic film image from these notations is often of poor quality. Crayon-type deposits of phosphors have similar limitations. The possibility of developing improved phosphorescent inks and/or ink dispensing devices is not discussed in U.S. Pat. No. 5,051,596 but the patent provides a useful context for the present invention, and is therefore incorporated herein by reference in its entirety.